.\" Copyright (c) 2012 Jeremie Le Hen <jlh@FreeBSD.org>
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.Dd June 29, 2023
.Dt LIBSTDBUF 3
.Os
.Sh NAME
.Nm libstdbuf
.Nd preloaded library to change standard streams initial buffering
.Sh DESCRIPTION
The
.Nm
library is meant to be preloaded with the
.Ev LD_PRELOAD
environment variable to as to change the initial buffering
of standard input, standard output and standard error streams.
.Pp
Although you may load and configure this library manually,
an utility,
.Xr stdbuf 1 ,
can be used to run a command with the appropriate environment variables.
.Sh ENVIRONMENT
Each stream can be configured independently through the following
environment variables (values are defined below):
.Bl -tag -width size -offset indent
.It Ev _STDBUF_I
Initial buffering definition for the standard input stream
.It Ev _STDBUF_O
Initial buffering definition for the standard output stream
.It Ev _STDBUF_E
Initial buffering definition for the standard error stream
.El
.Pp
Each variable may take one of the following values:
.Bl -tag -width size -offset indent
.It Qq 0
unbuffered
.It Qq L
line buffered
.It Qq B
fully buffered with the default buffer size
.It Ar size
fully buffered with a buffer of
.Ar size
bytes (suffixes 'k', 'M' and 'G' are accepted)
.El
.Sh EXAMPLE
In the following example, the stdout stream of the
.Xr awk 1
command
will be fully buffered by default because it does not refer
to a terminal.
.Nm
is used to force it to be line-buffered so
.Xr vmstat 8 Ns 's
output will not stall until the full buffer fills.
.Bd -literal -offset indent
# vmstat 1 | LD_PRELOAD=/usr/lib/libstdbuf.so \\
    STDBUF_1=L awk '$2 > 1 || $3 > 1' | cat -n
.Ed
.Pp
See
.Xr stdbuf 1
for a simpler way to do this.
.Sh SEE ALSO
.Xr rtld 1 ,
.Xr stdbuf 1
.Sh HISTORY
The
.Nm
library first appeared in
.Fx 8.4 .
.Sh AUTHORS
.An -nosplit
The original idea of the
.Nm
command comes from
.An Padraig Brady
who implemented it in the GNU coreutils.
.An Jeremie Le Hen
implemented it on
.Fx .
